Self-diffusion coefficients of oxygen ion in single crystals of MgO · <i>n</i> Al2O3 spinels

Abstract

Oxygen self-diffusion coefficients in single crystal spinels were determined for three compositions of MgO · Al2O3, MgO · 1.2Al2O3, and MgO · 2.2Al2O3 by a gas-solid exchange technique utilizing 18O as a tracer. The temperature dependence of the self-diffusion coefficient for MgO · Al2O3 was expressed as D = 0.89 exp(− 105 × 103/RT) cm2/sec. The self-diffusion coefficients for MgO · 1.2Al2O3 and MgO · 2.2Al2O3 were close to that for MgO · Al2O3, which was interpreted as being due to intrinsic diffusion. The determined self-diffusion coefficient of oxygen ion was smaller by several orders of magnitude than that of magnesium ion and was closer to the apparent diffusion coefficients calculated from the sintering rates. The influence of surface exchange reaction was noticed in determining the self-diffusion coefficient.